Engine

ABSTRACT

An engine includes a combustion chamber, a cylinder head, an intake valve, a partition wall plate, and a tumble valve. The cylinder head includes an intake port that communicates with the combustion chamber. The intake valve includes a head configured to open and close an open end of the intake port. The partition wall plate partitions the intake port into first and second passages. The tumble valve is configured to open and close either one of the first passage and the second passage. A cross sectional shape of the partition wall plate is defined on a basis of a shape of a gap that is surrounded by a contour of the head and a contour of the open end, as viewed in a reference direction. The reference direction is a direction from a reference point in the intake port to a gap between the open end and the head.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority from Japanese Patent ApplicationNo. 2020-096648 filed on Jun. 3, 2020, the entire contents of which arehereby incorporated by reference.

BACKGROUND

The disclosure relates to an engine including a combustion chamber.

To increase the thermal efficiency of an engine, a tumble flow isgenerated in a combustion chamber. Techniques for generating a tumbleflow are known (refer to Japanese Unexamined Patent ApplicationsPublication Nos. 2001-193469, H6-167220, and 2017-150379). In thesetechniques, a partition wall plate for defining a passage is provided inan intake port that introduces intake air into a combustion chamber.This partition wall plate adjusts a flow direction and a flow velocityof the intake air, whereby it is possible to generate a tumble flow inthe combustion chamber, resulting in improvement in thermal efficiency.

SUMMARY

An aspect of the disclosure provides an engine including a combustionchamber, a cylinder head, an intake valve, a partition wall plate, and atumble valve. The cylinder head includes an intake port thatcommunicates with the combustion chamber. The intake valve includes ahead that is configured to open and close an open end of the intakeport. The partition wall plate partitions the intake port into a firstpassage and a second passage. The tumble valve is configured to open andclose one of the first passage and the second passage. A cross sectionalshape of the partition wall plate is defined on a basis of a shape of agap that is surrounded by a contour of the head and a contour of theopen end, as viewed in a reference direction. The reference direction isa direction from a reference point in the intake port to a gap betweenthe open end and the head.

An aspect of the disclosure provides an engine including a combustionchamber, a cylinder head, a first intake valve, a second intake valve, apartition wall plate, and a tumble valve. The cylinder head includes anintake port that includes a common port section branching off into afirst port section and a second port section. The first intake valve isconfigured to open and close a first open end of the first port sectionthat communicates with the combustion chamber. The second intake valveis configured to open and close a second open end of the second portsection that communicates with the combustion chamber. The partitionwall plate partitions the intake port into a first passage and a secondpassage. The tumble valve is configured to open and close the firstpassage.

The partition wall plate includes a common plate section positioned atthe common port section, a first plate section positioned at the firstport section, and a second plate section positioned at the second portsection. The second passage at the common port section, which is definedby the common plate section, includes a width-direction center parthaving a passage cross sectional area larger than a passage crosssectional area of a width-direction outer part. The second passage atthe first port section, which is defined by the first plate section,includes a width-direction inner part having a passage cross sectionalarea larger than a passage cross sectional area of a width-directionouter part. The second passage at the second port section, which isdefined by the second plate section, includes a width-direction innerpart having a passage cross sectional area larger than a passage crosssectional area of a width-direction outer part.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the disclosure and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments and,together with the specification, serve to explain the principles of thedisclosure.

FIG. 1 is a schematic diagram illustrating an engine according to anembodiment of the disclosure.

FIG. 2 simply illustrates an intake port and a combustion chamber.

FIG. 3 simply illustrates an inside of the intake port from an arrow Z1direction in FIG. 2.

FIG. 4A simply illustrates a coordinate system of the combustionchamber.

FIG. 4B simply illustrates flows of intake air in the combustionchamber.

FIGS. 5A and 5B simply illustrate each dimension relating to thecombustion chamber and a cylinder bore.

FIG. 6A illustrates an example of a length in a circumferentialdirection of a yz cross section.

FIG. 6B illustrates an example of a flow velocity distribution of intakeair.

FIG. 7A is a sectional view along a line a-a in FIG. 2.

FIG. 7B is a sectional view along a line b-b in FIG. 2.

FIG. 7C is a sectional view along a line c-c in FIG. 2.

FIG. 8 illustrates a flow velocity distribution of intake air flowingfrom the intake port into the combustion chamber.

FIG. 9 illustrates an example of a coordinate plane set in thecombustion chamber.

FIG. 10 illustrates an example of a lift curve of an intake valve.

FIG. 11A illustrates a gap between the intake port and the intake valve.

FIG. 11B illustrates contours of the intake port and the intake valve.

FIG. 11C illustrates a shape of the gap between the intake port and theintake valve.

FIG. 12 simply illustrates the intake port and the combustion chamber.

FIG. 13A illustrates the shapes of the gaps between the intake port andthe intake valves.

FIG. 13B illustrates an ideal flow velocity distribution of the intakeair in the combustion chamber.

FIG. 13C illustrates an ideal flow velocity distribution of the intakeair flowing from the intake port into the combustion chamber.

FIG. 14A illustrates an ideal flow velocity distribution of the intakeair flowing from the intake port into the combustion chamber.

FIG. 14B illustrates shapes of open ends of the intake port.

FIG. 14C illustrates cross sectional shapes of first and second platesections of a partition wall plate.

FIG. 15 simply illustrates an intake port and a combustion chamber thatare provided to an engine according to another embodiment of thedisclosure.

FIG. 16 simply illustrates an inside of the intake port from an arrow Z1direction in FIG. 15.

FIG. 17A is a sectional view along a line a-a in FIG. 15.

FIG. 17B is a sectional view along a line b-b in FIG. 15.

FIG. 17C is a sectional view along a line c-c in FIG. 15.

FIG. 18A illustrates an ideal flow velocity distribution of the intakeair flowing from the intake port into the combustion chamber.

FIG. 18B illustrates shapes of open ends of the intake port.

FIG. 18C illustrates cross sectional shapes of first and second platesections of a partition wall plate.

DETAILED DESCRIPTION

The thermal efficiency of an engine is constantly desired to beimproved. For this reason, the shape of a partition wall plate is moresuitably set in order to generate a strong tumble flow in a combustionchamber.

It is desirable to generate a strong tumble flow in a combustionchamber.

In the following, some embodiments of the disclosure are described indetail with reference to the accompanying drawings. Note that thefollowing description is directed to illustrative examples of thedisclosure and not to be construed as limiting to the disclosure.Factors including, without limitation, numerical values, shapes,materials, components, positions of the components, and how thecomponents are coupled to each other are illustrative only and not to beconstrued as limiting to the disclosure. Further, elements in thefollowing example embodiments which are not recited in a most-genericindependent claim of the disclosure are optional and may be provided onan as-needed basis. The drawings are schematic and are not intended tobe drawn to scale.

Throughout the present specification and the drawings, elements havingsubstantially the same function and configuration are denoted with thesame numerals to avoid any redundant description.

Note that an engine 10 illustrated in the drawings is ahorizontally-opposed engine, but not limited thereto, and theembodiments of the disclosure can be used in an inline engine, a Vengine, or other type of engine.

Structure of Engine

FIG. 1 is a schematic diagram illustrating the engine 10 according to anembodiment of the disclosure. As illustrated in FIG. 1, the engine 10includes a cylinder block 11 provided to one cylinder bank, a cylinderblock 12 provided to the other cylinder bank, and a crankshaft 13supported by the pair of the cylinder blocks 11 and 12. Each of thecylinder blocks 11 and 12 has a cylinder bore 14 that houses a piston15. The piston 15 is coupled to the crankshaft 13 via a connecting rod16.

Each of the cylinder blocks 11 and 12 is assembled with a cylinder head18 that has a valve driving mechanism 17. The cylinder head 18 isassembled with a head cover 19 that covers the valve driving mechanism17. The cylinder head 18 includes an intake port 21 that communicateswith a combustion chamber 20, and the cylinder head 18 is assembled withan intake valve 22 that opens and closes the intake port 21. Thecylinder head 18 also includes an exhaust port 23 that communicates withthe combustion chamber 20, and the cylinder head 18 is assembled with anexhaust valve 24 that opens and closes the exhaust port 23.

Moreover, the cylinder head 18 is assembled with a valve unit 25 and anintake manifold 26, and intake air is guided to the intake port 21 viathese intake manifold 26 and valve unit 25. As described later, thevalve unit 25 is provided with a tumble valve 27, called tumblegeneration valve (TGV) and so on, in order to generate a tumble flow inthe combustion chamber 20. The cylinder head 18 is assembled with anexhaust manifold, which is not illustrated, and exhaust gas from theexhaust port 23 is guided via the exhaust manifold to a catalyticconverter and other components, which are not illustrated.

Structure of Inlet System

An inlet system for guiding intake air to the combustion chamber 20 willbe described. FIG. 2 simply illustrates the intake port 21 and thecombustion chamber 20. FIG. 3 simply illustrates the inside of theintake port 21 from the arrow Z1 direction in FIG. 2. Note that the pairof the intake valves 22, which are assembled to the cylinder head 18,are respectively represented as a “first intake valve 61” and a “secondintake valve 62” in the following descriptions.

As illustrated in FIGS. 1 to 3, the intake port 21 of the cylinder head18 has a common port section 33 on an upstream side, a first portsection 31 that is branched off from the common port section 33, and asecond port section 32 that is branched off from the common port section33. The intake port 21, which thus branches off to the combustionchamber 20, is provided with a partition wall plate 50 that partitionsthe inside of the intake port 21 into a first passage 41 on a head cover19 side and a second passage 42 on a side of a cylinder block 11 or 12.The partition wall plate 50 has a common plate section 53 that iscontained in the common port section 33, a first plate section 51 thatis contained in the first port section 31, and a second plate section 52that is contained in the second port section 32.

As illustrated in FIGS. 2 and 3, an open end 31 a of the first portsection 31 is opened and closed by a head 61 a of the first intake valve61, and an open end 32 a of the second port section 32 is opened andclosed by a head 62 a of the second intake valve 62. In one example, theopen end 31 a may serve as a “first open end”, and the open end 32 a mayserve as a “second open end”. In addition, an end 51 a of the firstplate section 51, which is contained in the first port section 31, ispositioned closer to the open end 31 a than a stem 61 b of the firstintake valve 61, and an end 52 a of the second plate section 52, whichis contained in the second port section 32, is positioned closer to theopen end 32 a than a stem 62 b of the second intake valve 62. Thepartition wall plate 50, which is provided in the intake port 21, may beprovided separately from the cylinder head 18 or may be integrated withthe cylinder head 18 into one body. In the case of integrating thepartition wall plate 50 with the cylinder head 18 into one body, thepartition wall plate may be integrated by casting or by using a 3Dprinter.

As illustrated in FIGS. 1 and 2, the valve unit 25, which is mounted tothe cylinder head 18, is provided with the tumble valve 27 that moves toa close position represented by the solid line and to an open positionrepresented by the broken line. As illustrated in FIG. 2, the tumblevalve 27 that is moved to the close position closes the first passage41, whereby intake air flowing from the intake manifold 26 into theintake port 21 is guided by the tumble valve 27 to the combustionchamber 20 via the second passage 42 of the intake port 21. In moredetail, moving the tumble valve 27 to the close position causes most ofintake air to pass through the second passage 42 of the intake port 21,as illustrated by the arrow F in FIG. 2, whereby the intake air flowsinto the combustion chamber 20 while being increased in flow velocity.Moreover, the intake air flows along the partition wall plate 50 andthereby advances to a gap G between the intake port 21 and the intakevalve 61. Thus, the intake air smoothly flows along an inner wall of thecombustion chamber 20, as illustrated by the arrow Ft, resulting ingeneration of a strong tumble flow in the combustion chamber 20 and inthe cylinder bore 14.

In this manner, the tumble valve 27, which generates a tumble flow inthe combustion chamber 20, is moved to the close position to narrow thepassage in the intake port 21, for example, in the case in which anengine load is low, and an intake air flow rate is low. With thisfunction, even in the situation in which the engine load is low, andflow velocity of intake air tends to decrease, it is possible toaggressively generate a tumble flow in the combustion chamber 20,whereby combustion efficiency of air-fuel mixture can be increased, andthermal efficiency of the engine 10 can be improved. On the other hand,for example, in the situation in which the engine load is high, and theintake air flow rate is high, the tumble valve 27 is moved to the openposition to open the first passage 41. This causes the intake air, whichflows from the intake manifold 26 into the intake port 21, to be guidedto the combustion chamber 20 via the first passage 41 and the secondpassage 42 of the intake port 21, whereby a lot of intake air issupplied to the combustion chamber 20.

Ideal Flow Velocity Distribution of Intake Air FIG. 4A simplyillustrates a coordinate system of the combustion chamber 20. FIG. 4Bsimply illustrates flows of intake air in the combustion chamber 20.FIGS. 5A and 5B simply illustrate each dimension relating to thecombustion chamber 20 and the cylinder bore 14. Note that, in FIGS. 4Ato 5B, parts of the combustion chamber 20 and the cylinder bore 14 areillustrated by a columnar shape, for easy explanation.

As illustrated in FIG. 4A, an x-axis, a y-axis, and a z-axis are set asmutually orthogonal coordinate axes that pass a center point C in anupper surface of the combustion chamber 20. The y-axis is a coordinateaxis parallel to a direction from the intake port 21 to the exhaust port23, which is a direction from the intake side to the exhaust side. Thez-axis is a coordinate axis coinciding with a center line of thecylinder bore 14. The x-axis is a coordinate axis orthogonal to both ofthe y-axis and the z-axis.

Herein, ideal tumble flows are tumble flows T1 and T2 that circulatealong cross sections Sa and Sb coinciding with or parallel to a yzcoordinate plane. That is, in order to increase thermal efficiency ofthe engine 10, it is desirable to generate a tumble flow that circulatesalong each cross section coinciding with or parallel to the yzcoordinate plane. Hereinafter, each cross section is described as a “yzcross section”. To generate such a tumble flow, intake air is made toflow in the combustion chamber 20 so that flow velocity will beproportional to a circulation distance of the tumble flow in each yzcross section, as described later.

From this point of view, a flow velocity distribution of intake air bywhich an ideal tumble flow is obtained, is investigated. Assuming that acirculation center of a tumble flow is at the center of each yz crosssection, and the tumble flow flows along an inner wall surface, acirculation distance of the tumble flow in each yz cross section differswith respect to each x coordinate. Herein, as illustrated by the arrowin FIG. 4B, the circulation distance of the tumble flow, which is alength L(x, θ) in the circumferential direction of each yz crosssection, is calculated based on the following formulas (1) and (2). Inthis case, as illustrated in FIGS. 5A and 5B, the symbol “B” representsa cylinder bore diameter, the symbol “H(θ)” represents a distance from acrown surface of the piston 15 to the upper surface of the combustionchamber 20, which varies in accordance with a crank angle θ.

$\begin{matrix}{{y(x)} = \sqrt{\left( \frac{B}{2} \right)^{2} - x^{2}}} & (1) \\{{L\left( {x,\ \theta} \right)} = {{{2 \cdot 2}{y(x)}} + {2\;{H(\theta)}}}} & (2)\end{matrix}$

FIG. 6A illustrates an example of the length L (x, θ) in thecircumferential direction of a yz cross section. FIG. 6B illustrates anexample of a flow velocity distribution V(x, θ) of intake air. Asillustrated in FIG. 6A, the length L(x, θ) in the circumferentialdirection of the yz cross section is shorter as x goes to a positiveside and to a negative side and is maximum when x=0. As described above,from the point of view of generating an ideal tumble flow, in order tomake the tumble flow circulate along each yz cross section, the flowvelocity distribution of the intake air in the x-axis direction isdesirably proportional to the length L(x, θ) in the circumferentialdirection. In other words, it is desirable that the flow velocity of theintake air is increased at a width-direction center part 20 a of thecombustion chamber 20, whereas the flow velocity of the intake air isdecreased at width-direction end parts 20 b of the combustion chamber20, as illustrated in FIG. 6B. The width-direction center part 20 a ofthe combustion chamber 20 is a center part in the x-axis direction ofthe combustion chamber 20, whereas the width-direction end parts 20 b ofthe combustion chamber 20 are both end parts in the x-axis direction ofthe combustion chamber 20. The flow velocity distribution V (x, θ) ofintake air, by which an ideal tumble flow is obtained, is calculatedbased on the following formula (3). Herein, the symbol “a” represents atime during which the tumble flow circulates in the combustion chamber20.

$\begin{matrix}{{V\left( {x,\theta} \right)} = \frac{L\left( {x,\theta} \right)}{a}} & (3)\end{matrix}$

Cross Sectional Shape of Partition Wall Plate

As described by using FIG. 6B, in order to generate an ideal tumbleflow, the flow velocity of the intake air is increased at thewidth-direction center part 20 a of the combustion chamber 20, whereasthe flow velocity of the intake air is decreased at the width-directionend parts 20 b of the combustion chamber 20. In consideration of this,the cross sectional shape of the partition wall plate 50, whichpartitions the inside of the intake port 21, is set so that the flowvelocity distribution of the intake air will be similar to the idealflow velocity distribution V (x, θ). Note that the alternate long andshort dash line illustrated in FIGS. 7B and 7C shows an example of apassage cross sectional area in each part in the passage 42.

FIG. 7A is a sectional view along a line a-a in FIG. 2. FIG. 7B is asectional view along a line b-b in FIG. 2. FIG. 7C is a sectional viewalong a line c-c in FIG. 2. As illustrated in FIG. 7A, an upstream end53 a of the partition wall plate 50 in the vicinity of the tumble valve27 is formed flat along a turn axis 27 a of the tumble valve 27. Inaddition, as illustrated in FIG. 7B, the common plate section 53 of thepartition wall plate 50 is bent in such a manner that a width-directioncenter part 53 b protrudes to the first passage 41. That is, in thesecond passage 42 of the common port section 33, which is defined by thecommon plate section 53, a passage cross sectional area 70 a of awidth-direction center part 70 is set larger than each of a passagecross sectional area 71 a of a width-direction outer part 71 and apassage cross sectional area 72 a of a width-direction outer part 72.The width-direction center part 70 and the width-direction outer parts71 and 72 illustrated in the drawing are obtained by trisecting thesecond passage 42 of the common port section 33 in the width direction.

As illustrated in FIG. 7C, the first plate section 51 of the partitionwall plate 50 is bent in such a manner that a width-direction inner part51 b protrudes to the first passage 41. That is, in the second passage42 of the first port section 31, which is defined by the first platesection 51, a passage cross sectional area 80 a of a width-directioninner part 80 is set larger than a passage cross sectional area 81 a ofa width-direction outer part 81. The second plate section 52 of thepartition wall plate 50 is bent in such a manner that a width-directioninner part 52 b protrudes to the first passage 41. That is, in thesecond passage 42 of the second port section 32, which is defined by thesecond plate section 52, a passage cross sectional area 82 a of awidth-direction inner part 82 is set larger than a passage crosssectional area 83 a of a width-direction outer part 83. Thewidth-direction inner part 80 and the width-direction outer part 81illustrated in the drawing are obtained by bisecting the second passage42 of the first port section 31 in the width direction. Thewidth-direction inner part 82 and the width-direction outer part 83illustrated in the drawing are obtained by bisecting the second passage42 of the second port section 32 in the width direction.

The cross sectional shape of the partition wall plate 50 forpartitioning the intake port 21 is set in this manner. Thus, in the casein which the tumble valve 27 is closed to guide the intake air to thesecond passage 42, a flow rate of the intake air flowing to thewidth-direction center part 20 a of the combustion chamber 20 isincreased, and flow velocity of the intake air is increased at thewidth-direction center part 20 a of the combustion chamber 20. In short,most of the intake air that flows into the intake port 21 via the valveunit 25, flows to the width-direction center part 70 of the common portsection 33. At this time, a lot of intake air flows at thewidth-direction inner part 80 of the first port section 31, and a lot ofintake air flows at the width-direction inner part 82 of the second portsection 32.

FIG. 8 illustrates a flow velocity distribution of the intake airflowing from the intake port 21 into the combustion chamber 20. Asdescribed above, a lot of intake air flows at the width-direction innerpart 80 of the first port section 31, and a lot of intake air flows atthe width-direction inner part 82 of the second port section 32. Thus,in a flow velocity distribution Vp1(x) of the intake air at the open end31 a of the first port section 31, flow velocity at the width-directioninner part 80 is higher than that at the width-direction outer part 81.Similarly, in a flow velocity distribution Vp2(x) of the intake air atthe open end 32 a of the second port section 32, flow velocity at thewidth-direction inner part 82 is higher than that at the width-directionouter part 83. As a result, also in a flow velocity distribution Vp3 (x)of intake air combined in the combustion chamber 20, flow velocity atthe width-direction center part 20 a is higher than flow velocities atthe width-direction end parts 20 b. That is, the flow velocitydistribution Vp3(x) of the intake air illustrated in FIG. 8 is similarto the flow velocity distribution V(x, θ) of the intake air illustratedin FIG. 6B, whereby a strong tumble flow can be generated in thecombustion chamber 20.

In addition, the end 51 a of the first plate section 51, which iscontained in the first port section 31, is positioned closer to the openend 31 a than the stem 61 b of the first intake valve 61, and the end 52a of the second plate section 52, which is contained in the second portsection 32, is positioned closer to the open end 32 a than the stem 62 bof the second intake valve 62. Thus, the partition wall plate 50 isextended to the vicinity of the open ends 31 a and 32 a. This enablesappropriately controlling the intake air immediately before the intakeair flows into the combustion chamber 20, resulting in generation of astrong tumble flow in the combustion chamber 20.

Procedure of Setting Cross Sectional Shape of Partition Wall Plate

Next, a procedure of setting a cross sectional shape of the partitionwall plate 50 will be described from the point of view of the ideal flowvelocity distribution V(x, θ) of the intake air. FIG. 9 illustrates anexample of a coordinate plane S1 set in the combustion chamber 20. FIG.10 illustrates an example of a lift curve of the intake valve 61 or 62.FIG. 11A illustrates a gap G between the intake port 21 and the intakevalve 61 or 62. FIG. 11B illustrates contours of the intake port 21 andthe intake valve 61 or 62. FIG. 11C illustrates a shape of the gapbetween the intake port 21 and the intake valve 61 or 62.

As illustrated in FIG. 9, a coordinate plane S1 is set in the vicinityof the open end 31 a or 32 a of the intake port 21. The coordinate planeS1 is orthogonal to a straight line L1 that extends from a referencepoint P1 in the intake port 21 to the gap G between the open end 31 a or32 a and the corresponding head 61 a or 62 a. The heads 61 a and 62 aillustrated in the drawing are opened by the maximum lift amount Lmax,which is illustrated in FIG. 10. The coordinate plane S1 contains anx-axis as a coordinate axis. This x-axis is a coordinate axis orthogonalto the direction from the intake port 21 to the exhaust port 23, whichis the arrow y direction from the intake side to the exhaust side. Notethat the following describes the coordinate axis indicated by the symbol“x” in FIG. 9, as the x-axis.

FIG. 11A illustrates the open ends 31 a and 32 a and the heads 61 a and62 a as viewed in a direction from the reference point P1 in the intakeport 21 to the gap G. In other words, FIG. 11A illustrates the open ends31 a and 32 a and the heads 61 a and 62 a as viewed in the directionfrom the reference point P1 along the straight line L1, which isillustrated in FIG. 9. In one example, this direction may serve as a“reference direction”. As illustrated by the arrow F in FIG. 2, most ofthe intake air flowing from the intake port 21 into the combustionchamber 20 passes through the gap G between the intake port 21 and theintake valve 61 or 62. In more detail, a gap G is provided between anexhaust side end 90 of the open end 31 a or 32 a and an exhaust side end91 of the corresponding head 61 a or 62 a, as illustrated by thehatching in FIG. 11A, and the intake air passes through this gap G toflow from the intake port 21 into the combustion chamber 20. Inconsideration of this, in order to control the flow rate and the flowvelocity of the intake air flowing in the combustion chamber 20, thecross sectional shapes of the first and second plate sections 51 and 52constituting the partition wall plate 50 are determined based on theshapes of the gaps surrounded by the contours of the open ends 31 a and32 a and the contours of the corresponding heads 61 a and 62 a.

From this point of view, in accordance with the following procedure, thecross sectional shapes of the first and second plate sections 51 and 52constituting the partition wall plate 50 are set based on the shapes ofthe gaps surrounded by the contours of the open ends 31 a and 32 a andthe contours of the corresponding heads 61 a and 62 a. Herein, thefunction f₁(x) illustrated in FIG. 11B specifies the contour of the openend 31 a or 32 a that is projected on the coordinate plane S1, based onx, the function f₂(x) illustrated in FIG. 11B specifies the contour ofthe head 61 a or 62 a that is projected on the coordinate plane S1,based on x, and the function f₃(x) illustrated in FIG. 11C specifies agap shape that is projected on the coordinate plane S1, based on x. Inother words, the gap shape f₃(x) illustrated in FIG. 11C is the shape ofthe gap surrounded by the contour of the open end 31 a or 32 a and thecontour of the corresponding head 61 a or 62 a. Thus, as illustrated inFIG. 9, the gap shape f₃(x) between the open end 31 a or 32 a and thecorresponding head 61 a or 62 a is calculated by subtracting the contourf₂(x) of the corresponding head 61 a or 62 a from the contour f₁(x) ofthe open end 31 a or 32 a. That is, the gap shape f₃(x) through whichthe intake air passes is calculated based on the following formula (4).Note that each shape is projected on the coordinate plane S1 along aline orthogonal to the coordinate plane S1.

f ₃(x)=f ₁(x)−f ₂(x)  (4)

FIG. 12 simply illustrates the intake port 21 and the combustion chamber20. As illustrated in FIG. 12, a straight line La connecting thereference point P1 in the intake port 21 and the exhaust side end 90 ofthe open end 31 a or 32 a is set, and a straight line Lb connecting thereference point P1 in the intake port 21 and the exhaust side end 91 ofthe head 61 a or 62 a is also set. In addition, it is assumed that anangle between the straight line La and a reference plane Sc isrepresented as “θ1”, and an angle between the straight line Lb and thereference plane Sc is represented as “θ2”. In these conditions, the gapshape f₃(x) may be calculated based on the following formula (5). Inthis case, the reference plane Sc is a flat plane orthogonal to thecenter line of the cylinder bore 14.

f ₃(x)=f ₂(x)·sin(θ₂−θ₁)  (5)

Then, an ideal flow velocity distribution F_(f)(x) of the intake airflowing from the intake port 21 into the combustion chamber 20 will bedescribed. FIG. 13A illustrates the shapes of the gaps between theintake port 21 and the intake valves 61 and 62. FIG. 13B illustrates anideal flow velocity distribution of the intake air in the combustionchamber 20. FIG. 13C illustrates an ideal flow velocity distribution ofthe intake air flowing from the intake port 21 to the combustion chamber20.

The function f₃(x) illustrated in FIG. 13A is the function f₃(x)illustrated in FIG. 11C and specifies each of the pair of the gap shapesthat are projected on the coordinate plane S1, based on x. The functionV(x) illustrated in FIG. 13B corresponds to the flow velocitydistribution V(x, θ) illustrated in FIG. 6B and specifies an ideal flowvelocity distribution of the intake air in the combustion chamber 20,which is projected on the coordinate plane S1, based on x. The flowvelocity distribution V(x) is a flow velocity distribution V(x, θ) at acertain crank angle θ. The function F_(f)(x) illustrated in FIG. 13Ccorresponds to the flow velocity distribution Vp1(x) or Vp2(x)illustrated in FIG. 8 and specifies an ideal flow velocity distributionof the intake air at the open end 31 a or 32 a, based on x.

The ideal flow velocity distribution F_(f)(x) at the open end 31 a or 32a illustrated in FIG. 13C is a flow velocity distribution at the timethe intake air passes through each of the pair of the gaps having thegap shape f₃(x), and the this ideal flow velocity distribution F_(f) (x)produces the ideal flow velocity distribution V(x) of the intake air inthe combustion chamber 20. Thus, the ideal flow velocity distributionF_(f)(x) at the open end 31 a or 32 a is calculated based on thefollowing formula (6). Note that, in the formula (6), the symbols “α”and “β” represent predetermined coefficients obtained by experiment,simulation, or other method.

F _(f)(x)=α·f ₃(x)×β·V(x)  (6)

Next, the cross sectional shape of the partition wall plate 50, which iscontained in the intake port 21, or more precisely, the cross sectionalshapes of the first and second plate sections 51 and 52, will bedescribed. FIG. 14A illustrates an ideal flow velocity distribution ofthe intake air flowing from the intake port 21 into the combustionchamber 20. FIG. 14B illustrates the shapes of the open ends 31 a and 32a of the intake port 21. FIG. 14C illustrates the cross sectional shapesof the first and second plate sections 51 and 52 of the partition wallplate 50.

The function F_(f)(x) illustrated in FIG. 14A is the function F_(f)(x)illustrated in FIG. 13C and specifies the ideal flow velocitydistribution of the intake air at the open end 31 a or 32 a, based on x.The function f_(po) (x) illustrated in FIG. 14B specifies the shape ofthe open end 31 a or 32 a that is projected on the coordinate plane S1,based on x. The function F_(p)(x) illustrated in FIG. 14C specifies thecross sectional shape of the first and second plate sections 51 and 52that is projected on the coordinate plane S1, based on x.

The cross sectional shape F_(p)(x) of the first and second platesections 51 and 52 illustrated in FIG. 14C determines the flow rate andthe flow velocity of the intake air at the corresponding open end 31 aor 32 a and also determines the ideal flow velocity distributionF_(f)(x) at the open end 31 a or 32 a. Thus, the cross sectional shapeF_(p)(x) of the first and second plate sections 51 and 52 is calculatedbased on the following formula (7). Note that, in the formula (7), thesymbols “γ” and “δ” represent predetermined coefficients obtained byexperiment, simulation, or other method.

F _(P)(x)=F _(f)(x)+γ·f _(PO)(x)+δ  (7)

As described above, the cross sectional shape F_(p)(x) of the first andsecond plate sections 51 and 52 constituting the partition wall plate 50is set based on the shape of the gap surrounded by the contour of theopen end 31 a or 32 a and the contour of the corresponding head 61 a or62 a, as viewed in the reference direction. Thus, the cross sectionalshape F_(p)(x) of the first plate section 51 or the second plate section52 is set so that the flow velocity distribution of the intake air inthe combustion chamber 20 will be similar to the ideal flow velocitydistribution V(x). As a result, as illustrated in FIG. 14C, the firstplate section 51 of the partition wall plate 50 is bent in such a mannerthat the width-direction inner part 51 b protrudes to the first passage41, and the second plate section 52 of the partition wall plate 50 isalso bent in such a manner that the width-direction inner part 52 bprotrudes to the first passage 41. This structure enables a lot ofintake air to flow at the width-direction inner part 80 of the firstport section 31 and also enables a lot of intake air to flow at thewidth-direction inner part 82 of the second port section 32. Thus, theflow velocity of the intake air at the width-direction center part 20 aof the combustion chamber 20 is increased, resulting in generation of astrong tumble flow.

The cross sectional shape F_(p)(x) of the partition wall plate 50 iscalculated by the following formula (8) that is derived by combining theformulas (6) and (7).

F _(P)(x)=α·f ₃(x)×β·V(x)+r·f _(PO)(x)+δ  (8)

Herein, the cross sectional shape “F_(p)(x)” of the partition wall plate50 is replaced with “f_(a)(x)”, the gap shape “f₃(x)” surrounded by thecontour of the head 61 a or 62 a and the contour of the correspondingopen end 31 a or 32 a is replaced with “f_(b)(x)”, the flow velocitydistribution “V(x)” of the intake air flowing into the combustionchamber 20 is replaced with “f_(c)(x)”, and the contour “f_(po)(x)” ofthe open end 31 a or 32 a is replaced with “f_(d)(x)”. Thus, the crosssectional shape f_(a)(x) of the partition wall plate 50 is calculated bythe following formula (9).

In other words, the cross sectional shape of the partition wall plate 50satisfies the following formula (9):

f _(a)(x)=α·f _(b)(x)×β·f _(c)(x)+γ·f _(d)(x)+δ  (9)

where

f_(a)(x) represents the cross sectional shape of the partition wallplate 50 that is projected on the coordinate plane S1,

f_(b)(x) represents a shape of the gap which is surrounded by thecontour of the head 61 a or 62 a and the contour of the correspondingopen end 31 a or 32 a and is projected on the coordinate plane S1,

f_(c)(x) represents the flow velocity distribution of the intake airflowing into the combustion chamber 20,

f_(d)(x) represents the contour of the open end 31 a or 32 a that isprojected on the coordinate plane S1, and

α, β, γ, and δ represent predetermined coefficients. Note that eachshape is projected on the coordinate plane S1 along a line orthogonal tothe coordinate plane S1.

Other Embodiments

FIG. 2 illustrates an example in which the first passage 41 on the headcover 19 side is closed by the tumble valve 27, but the embodiment isnot limited thereto, and the second passage 42 on the side of thecylinder block 11 or 12 may be closed by the tumble valve 27. FIG. 15simply illustrates the intake port 21 and the combustion chamber 20 thatare provided to an engine 100 according to another embodiment of thedisclosure. FIG. 16 simply illustrates the inside of the intake port 21from the arrow Z1 direction in FIG. 15. FIG. 17A is a sectional viewalong a line a-a in FIG. 15. FIG. 17B is a sectional view along a lineb-b in FIG. 15. FIG. 17C is a sectional view along a line c-c in FIG.15. Note that the same sections and parts as those illustrated in FIGS.2 and 7 are denoted by the same reference symbols in FIGS. 15 and 17,and descriptions thereof are omitted.

As illustrated in FIG. 15, the intake port 21, which branches off to thecombustion chamber 20, is provided with a partition wall plate 110 thatpartitions the inside of the intake port 21 into a first passage 101 onthe side of the cylinder block 11 or 12 and a second passage 102 on thehead cover 19 side. The partition wall plate 110 has a common platesection 113 that is contained in the common port section 33, a firstplate section 111 that is contained in the first port section 31, and asecond plate section 112 that is contained in the second port section32. In addition, an end 111 a of the first plate section 111, which iscontained in the first port section 31, is positioned closer to the openend 31 a than the stem 61 b of the first intake valve 61, and an end 112a of the second plate section 112, which is contained in the second portsection 32, is positioned closer to the open end 32 a than the stem 62 bof the second intake valve 62.

As illustrated in FIG. 15, moving the tumble valve 27 to the closeposition causes most of the intake air to pass through the secondpassage 102 of the intake port 21, as illustrated by the arrow F,whereby the intake air flows into the combustion chamber 20 while beingincreased in flow velocity. Moreover, the intake air flows along thepartition wall plate 110 and thereby advances to the gap G between theintake port 21 and the intake valve 61 or 62. Thus, the intake airsmoothly flows along an inner wall of the combustion chamber 20, asillustrated by the arrow Ft, resulting in generation of a strong tumbleflow in the combustion chamber 20 and in the cylinder bore 14.

As illustrated in FIG. 17A, an upstream end 113 a of the partition wallplate 110 in the vicinity of the tumble valve 27 is formed flat alongthe turn axis 27 a of the tumble valve 27. In addition, as illustratedin FIG. 17B, the common plate section 113 of the partition wall plate110 is bent in such a manner that a width-direction center part 113 bprotrudes to the first passage 101. That is, in the second passage 102of the common port section 33, which is defined by the common platesection 113, a passage cross sectional area 120 a of a width-directioncenter part 120 is set larger than each of a passage cross sectionalarea 121 a of a width-direction outer part 121 and a passage crosssectional area 122 a of a width-direction outer part 122. Thewidth-direction center part 120 and the width-direction outer parts 121and 122 illustrated in the drawing are obtained by trisecting the secondpassage 102 of the common port section 33 in the width direction.

As illustrated in FIG. 17C, the first plate section 111 of the partitionwall plate 110 is bent in such a manner that a width-direction innerpart protrudes to the first passage 101. That is, in the second passage102 of the first port section 31, which is defined by the first platesection 111, a passage cross sectional area 130 a of a width-directioninner part 130 is set larger than a passage cross sectional area 131 aof a width-direction outer part 131. The second plate section 112 of thepartition wall plate 110 is bent in such a manner that a width-directioninner part protrudes to the first passage 101. That is, in the secondpassage 102 of the second port section 32, which is defined by thesecond plate section 112, a passage cross sectional area 132 a of awidth-direction inner part 132 is set larger than a passage crosssectional area 133 a of a width-direction outer part 133. Thewidth-direction inner part 130 and the width-direction outer part 131illustrated in the drawing are obtained by bisecting the second passage102 of the first port section 31 in the width direction. Thewidth-direction inner part 132 and the width-direction outer part 133illustrated in the drawing are obtained by bisecting the second passage102 of the second port section 32 in the width direction.

The cross sectional shape of the partition wall plate 110 forpartitioning the intake port 21 is set in this manner. Thus, in the casein which the tumble valve 27 is closed to guide the intake air to thesecond passage 102, the flow rate of the intake air flowing to thewidth-direction center part 20 a of the combustion chamber 20 isincreased, and the flow velocity of the intake air is increased at thewidth-direction center part 20 a of the combustion chamber 20. In short,most of the intake air that flows into the intake port 21 via the valveunit 25, flows to the width-direction center part 120 of the common portsection 33. At this time, a lot of intake air flows at thewidth-direction inner part 130 of the first port section 31, and a lotof intake air flows at the width-direction inner part 132 of the secondport section 32, resulting in generation of a strong tumble flow in thecombustion chamber 20.

FIG. 18A illustrates an ideal flow velocity distribution F_(f)(x) of theintake air flowing from the intake port 21 into the combustion chamber20. FIG. 18B illustrates the shapes f_(po)(x) of the open ends 31 a and32 a of the intake port 21. FIG. 18C illustrates the cross sectionalshapes F_(p)(x) of the first and second plate sections 111 and 112 ofthe partition wall plate 110. As illustrated in FIG. 15, also in thecase in which the first passage 101 is closed by the tumble valve 27 toallow most of the intake air to flow in the second passage 102, thecross sectional shape of the partition wall plate 110 can be set byusing the formula (7). That is, as illustrated in FIGS. 18A to 18C, thecross sectional shape F_(p)(x) of the first and second plate sections111 and 112 can be set based on the formula (7) by using the ideal flowvelocity distribution F_(f)(x) at the corresponding open end 31 a or 32a and the shape f_(po)(x) of the corresponding open end 31 a or 32 a ofthe intake port 21.

It is needless to say that the disclosure is not limited to theforegoing embodiments and various modifications can be made theretowithin the scope that does not depart from the gist thereof. In oneexample, although the cross sectional shape of the intake port 21illustrated in FIGS. 7 and 17 is a rounded quadrangular shape, the crosssectional shape is not limited thereto and can be any shape such as acircle or an ellipse. In another example, although the contour f₂(x) ofthe head 61 a or 62 a illustrated in FIG. 9 represents a contour of theintake valve 61 or 62 opened by the maximum lift amount, the contour isnot limited thereto and can be a contour of the intake valve 61 or 62opened by another lift amount.

1. An engine comprising: a combustion chamber; a cylinder headcomprising an intake port that communicates with the combustion chamber;an intake valve comprising a head that is configured to open and closean open end of the intake port; a partition wall plate partitioning theintake port into a first passage and a second passage; and a tumblevalve configured to open and close either one of the first passage andthe second passage, wherein a cross sectional shape of the partitionwall plate is defined on a basis of a shape of a gap that is surroundedby a contour of the head and a contour of the open end, as viewed in areference direction, the reference direction being a direction from areference point in the intake port to a gap between the open end and thehead.
 2. The engine according to claim 1, wherein the cross sectionalshape of the partition wall plate satisfies the following formula:f _(a)(x)=α·f _(b)(x)×β·f _(c)(x)+γ·f _(d)(x)+δ where an x-axisrepresents a coordinate axis that is contained in a coordinate planeorthogonal to a straight line from the reference point in the intakeport to the gap between the open end and the head and that is orthogonalto a direction from an intake side to an exhaust side of the combustionchamber, f_(a)(x) represents a cross sectional shape of the partitionwall plate that is projected on the coordinate plane, f_(b) (x)represents the shape of the gap that is surrounded by the contour of thehead and the contour of the open end and that is projected on thecoordinate plane, f_(c)(x) represents a flow velocity distribution ofintake air flowing into the combustion chamber, f_(d)(x) represents thecontour of the open end that is projected on the coordinate plane, andα, β, γ, and δ represent predetermined coefficients.
 3. An enginecomprising: a combustion chamber; a cylinder head comprising an intakeport that comprises a common port section branching off into a firstport section and a second port section; a first intake valve configuredto open and close a first open end of the first port section thatcommunicates with the combustion chamber; a second intake valveconfigured to open and close a second open end of the second portsection that communicates with the combustion chamber; a partition wallplate partitioning the intake port into a first passage and a secondpassage; and a tumble valve configured to open and close the firstpassage, wherein the partition wall plate comprises a common platesection positioned at the common port section, a first plate sectionpositioned at the first port section, and a second plate sectionpositioned at the second port section, the second passage at the commonport section, which is defined by the common plate section, comprises afirst width-direction outer part, and a first width-direction centerpart having a passage cross sectional area larger than a passage crosssectional area of the first width-direction outer part, the secondpassage at the first port section, which is defined by the first platesection, comprises a second width-direction outer part, and a secondwidth-direction inner part having a passage cross sectional area largerthan a passage cross sectional area of the second width-direction outerpart, and the second passage at the second port section, which isdefined by the second plate section, comprises a third width-directionouter part, and a third width-direction inner part having a passagecross sectional area larger than a passage cross sectional area of thethird width-direction outer part.
 4. The engine according to claim 3,wherein the first plate section comprises an end that is positionedcloser to the first open end than a stem of the first intake valve, andthe second plate section has an end that is positioned closer to thesecond open end than a stem of the second intake valve.